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Articles in PresS, published online ahead of print September 27, 2001
Am J Physiol Heart Circ Physiol, 10.1152/ajpheart.00672.2001
Submitted on July 30, 2001
Accepted on September 19, 2001
1 Exp. Cardiovascular Biology, IRCM, Montreal, Quebec, Canada
2 Cardiology, University of Toronto, Toronto, Ontario, Canada
* To whom correspondence should be addressed. E-mail: deschec{at}ircm.qc.ca.
We have previously reported that the left ventricular mass (LVM) of WKHA rats was higher than that of WKY in the absence of a difference in systolic blood pressure. To extend these earlier observations, we conducted a series of functional and morphological investigations on both strains. Analysis of tissue sections revealed that the surface of ventricular tissue from WKHA was higher than that of WKY, without any enlargement of the cavity area. Analysis of isolated adult cells showed that cell width (as well as cell volume) of ventricular cardiomyocytes was significantly higher in WKHA than in WKY rats. However, the left ventricles of WKHA contained about 33% less cardiomyocytes than that from WKY. Mean intracellular free calcium concentration of cardiomyocytes was also higher in WKHA than in WKY. Hemodynamic measurements revealed that the values of dP/dt were higher in LV from WKHA. However, these differences were reduced (dP/dt-) or abolished (dP/dt+) when the values were normalized for both number and mean cross-sectional area of ventricular cardiomyocytes. Mean levels of systolic and diastolic blood pressure (corresponding to the 24 hour-average of measurements obtained continuously in conscious unrestrained animals using radiotelemetric implants) were not different between strains. However, circadian rhythm was more evident in WKY rats, as the difference between morning and night values of systolic and diastolic blood pressure was greater (by 3 mm Hg) in WKY. Altogether, our data validate the use of WKHA rats as models of predominantly concentric LV hypertrophy developing in the absence of changes in mean levels of hemodynamic cardiac load, and show that the hypertrophy phenotype is more pronounced in isolated cardiomyocytes than at that the level of the whole ventricle.
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